This type of lifetime subscription does not exist any more for devices that come after Xperia 10 III.
But you can always pay 4.99eur for one month, and then stop your subscription until you want to have access to another update and pay again 4.99 at that moment.
In the meanwhile, while updates will not be available while your subscription is paused, you will still keep access to Android App Support and other goodies (Microsoft and typing support).
You can read about how it is in this thread (see the ‘solved’ answer):